This invention relates to an electrostatic chuck member used when a conductive member, a semiconductive member, an insulative member or the like is held at adsorption state by static electricity, and a method of producing the same.
Recently, treatments such as dry etching, ion implantation, CVD, PVD and the like constituting a part of a production process for semiconductor or liquid crystal display, e.g. a production device of semiconductors changes from a wet process into a dry process from viewpoints of automation and anti-pollution. A greater part of the treatment through the dry process is usually carried out under vacuum or in an atmosphere under a reduced pressure.
In such a dry process treatment, it is required to improve a positioning accuracy in the formation of patterns on a substrate such as a silicon wafer, a glass plate or the like from viewpoints of high integration of circuits and fine work.
As a method satisfying such a demand, vacuum chuck or mechanical chuck has hitherto been utilized in the transportation, adsorption and fixation of the substrate. However, since the vacuum chuck is used under vacuum, the pressure difference is not made large and the adsorption force is weak. Even if the substrate can be adsorbed, an adsorbing portion becomes local and strain is caused in the substrate. Furthermore, the gas cooling can not be carried out with the temperature rising in the treatment of the wafer, so that the vacuum chuck can not be applied to the recent production process of high-performance semiconductor devices. On the other hand, the mechanical chuck becomes complicated in the structure and takes a long time in the maintenance and inspection thereof.
In order to avoid the above drawbacks of the conventional technique, electrostatic chuck utilizing static electricity is recently developed and widely adopted. However, this technique has the following problems.
When the substrate is adsorbed and held by such an electrostatic chuck, charge retains between the substrate and the electrostatic chuck (through the action of adsorption force) even after the applied voltage is topped, so that the detaching of the substrate can not be carried out unless the charge is completely removed.
For this end, it has been attempted to improve the insulating dielectric material used in the electrostatic chuck. For example, there are the following proposals:
{circle around (1)} JP-A-6-8089 discloses an example of using a sintered body or a spray coating of a mixture of aluminum nitride powder and titanium nitride powder as a high insulative material;
{circle around (2)} JP-A-6-302677 discloses that titanium oxide is applied onto a surface of the high insulative material and aluminum is applied thereto to contact with Si+SiC plate;
{circle around (3)} JP-B-6-36583 discloses an example using aluminum oxide as a high insulative material;
{circle around (4)} JP-A-5-235152 and JP-A-6-8089 disclose that aluminum oxide, aluminum nitride, zinc oxide, quartz, boron nitride, sialon and the like are used as a high insulative material;
{circle around (5)} JP-A-3-147843 and JP-A-3-204924 disclose a method wherein volume resistivity is lowered to improve static electricity by adding TiO2 having a high dielectric constant to the high insulative material in case of further requiring a higher static electricity;
{circle around (6)} The high insulative material of Al2O3 or the like containing TiO2 has a drawback that adsorption force remains for an interim even after the power source is switched off. As a technique overcoming this drawback, therefore, JP-A-11-111826, JP-A-11-69855 and the like disclose a method wherein a polarity of an electrode is reversed for shortening a detaching time of a silicon wafer;
{circle around (7)} JP-A-8-64663 discloses a method wherein a coating having a conductivity is formed on a part of an insulating layer for rapidly conducting the detaching of the silicon wafer;
{circle around (8)} JP-A-8-330403, JP-A-11-26564 and the like disclose an electrostatic chuck member having a water-cooling structure for preventing temperature rise of the electrostatic chuck in the operation and the lowering of performances accompanied therewith.
However, a Al2O3xe2x80x94TiO2 based high insulative spray-coated layer used in the electrostatic chuck has the following problems to be solved.
(1) In the Al2O3 based spray-coated layer mixed with TiO2, the volume resistivity is small and a slight current flows, so that it can be expected to improve the static electricity through Jensen-Rahbek effect (A. Jensen and K. Rahbek s force). However, since TiO2 is a semiconductor substance, the moving rate of electrical charge is slow and the responsibility (arrival time of saturated adsorption, adsorption disappearing time) when the application of voltage is stopped is poor, and this responsibility becomes more remarkable under low-temperature environment.
In order to render the value of volume resistivity into, for example, a practical state of 1xc3x97109 xcexa9xc2x7cm, it is necessary to add about 25 wt % of TiO2. In the production process of semiconductors, however, the addition of a great amount of TiO2 means the incorporation of impurity, which brings about the degradation of quality and results in the contamination of working environment.
Furthermore, when the temperature of the semiconductor wafer to be adsorbed is higher than room temperature, there is a high possibility that a large leak current is passed to break wafer circuit because the volume resistivity is too low.
(2) The Al2O3.TiO2 based spray-coated layer is formed by a spraying process. In the coating obtained by this method, however, the volume resistivity and adsorption force are largely scattered and also the productivity is low to bring about the rise of the cost.
It is, therefore, a main object of the invention to provide an electrostatic chuck member having a large volume resistivity, a small scattering thereof and a good quality.
It is another object of the invention to provide an electrostatic chuck member having a strong adsorption force and an excellent responsibility (release property) in the stop of voltage application.
It is the other object of the invention to provide a spray-coated layer for an electrostatic chuck member without TiO2 damaged by contact with a silicon wafer, a physical erosion action through plasma or a chemical erosion action through a halogen compound included in an environment and fearing a pollution of environment.
It is a still further object of the invention to propose a substitute technique for overcoming such a drawback that the conventional Al2O3 insulative substrate produced by the sintering process is easily damaged by a temperature change in a use environment.
It is a yet further object of the invention to form a greater part of not only an insulating layer but also an electrode by a spraying method to develop a high productivity, a good coating adhesion property and an excellent static electricity for overcoming drawbacks inherent to the conventional electrostatic chuck member formed by spraying a ceramic around a metal electrode.
An electrostatic chuck member according to the invention is formed by laminating a metallic electrode layer and an insulating layer of an oxide ceramic having an electric resistance onto a surface of a metal substrate through spraying.
That is, a basic construction of the invention is an electrostatic chuck member comprising a substrate, a metallic undercoat formed on at least one surface thereof, a lower insulating layer of Al2O3 ceramic formed on the undercoat, a metallic electrode layer formed on the lower insulating layer and an upper insulating layer of Al2O3 ceramic formed on the electrode layer as a topcoat.
In the invention, the metallic undercoat is a spray-coated layer having a thickness of 30-300 xcexcm, and each of the lower insulating layer and the upper insulating layer is a spray-coated layer having a thickness of 100-500 xcexcm, and the metallic electrode layer is a spray-coated layer having a thickness of 5-100 xcexcm and is favorable to have an oxygen amount included in the metallic electrode layer of not more than 2.0 wt % and a porosity of 1-7%.
Each of the lower and upper insulating layers made of Al2O3 ceramic is preferable to be formed by spraying a spraying material powder having a purity of not less than 98.0 wt % so as to render the porosity into a range of 1-8%.
It is favorable that at least one surface of each of the lower insulating layer and the upper insulating layer is sealed by impregnating an organic or inorganic silicon compound and a volume resistivity of such a layer is within a range of 1xc3x971013-1xc3x971015 xcexa9xc2x7cm.
The metallic electrode layer is favorable to be formed using at least one spraying material selected from W, Al, Cu, Nb, Ta, Mo, Ni and alloys containing at least one of these metallic elements.
The metallic undercoat applied between the substrate and the lower insulating layer of Al2O3 ceramic for improving a bonding force therebetween is favorable to be formed by using at least one spraying material selected from Ni, Al, Cr, Co, Mo and an alloy containing at least one of these metallic elements.
The upper insulating layer of Al2O3 occupied as a topcoat in an outermost surface layer portion of the electrostatic chuck member according to the invention is preferable to be finished a contact face with a silicon wafer supported thereon to a surface roughness Ra: about 0.1-2.0 xcexcm by mechanical working.
As a spraying process used in the production of the electrostatic chuck member according to the invention, any one of low-speed and high-speed flame spraying process, arch spraying process, atmosphere plasma spraying process, plasma spraying process under a reduced pressure, explosion spraying process and the like may be used in the formation of the metallic undercoat. On the other hand, it is favorable to adopt atmosphere plasma spraying process, plasma spraying process under a reduced pressure or the like in the formation of the Al2O3 ceramic insulating coated-film.
Although the example of film formation is described by limiting only the spraying process in the invention, it is possible to conduct similar film-forming means such as CVD, PVD, ion implantation and the like, if necessary.